1. Field of the Invention
The present invention relates to a laser diode (LD) driver for driving an LD in an optical recording and reproducing apparatus, and more particularly, to an apparatus, which has an auto laser power control (ALPC) function and can drive two or more LDs using the LD driver, a method of driving the LD driver, and a method of initializing the optical recording and reproducing apparatus.
2. Description of the Related Art
FIG. 1 illustrates the structure of a laser diode (LD) driver 100 for driving an LD (not shown) currently used in optical recording apparatuses.
The components of the LD driver 100 include switches 10a through 10c, a multiplexer 12 for multiplexing the outputs of the switches 10a through 10c, an amplifier 14 for amplifying the output of the multiplexer 12 with a predetermined degree of amplification, an adder 16, and a high frequency modulator (HFM) 18.
Current such as peak current, bias current, and read current, or voltage correspond to power levels such as peak power level, bias or erase power level, and read power level of the LD, which are applied to the switches 10a through 10c. The power levels are turned on and off by control signals such as peak control, bias control, and read control.
The outputs of the switches 10a through 10c are multiplexed by the multiplexer 12. The output of the multiplexer 12 is applied to a recording medium. Because the LD cannot be fully driven by the output of the multiplexer 12 alone, the output of the multiplexer 12 is amplified through the amplifier 14.
The HFM 18 generates a high frequency modulation signal to remove optical interference noise from an optical pick-up (not shown). The adder 16 adds the high frequency modulation signal to the output of the amplifier 14 and outputs a driving signal to the LD. The LD, in turn, generates a recording signal corresponding to the driving signal from the adder 16. Here, the high frequency modulation signal is set to have the most effective frequency and magnitude for removing the optical interference noise and is primarily used in a read mode. Further, in the LD driver 100, the number of switches may include two to five switches according to the number of channels used (2ch through 5ch), which are the number of driving levels in a recording signal.
The LD changes according to an operating temperature. Specifically, referring to FIG. 2, an output characteristic of TOLD9452MB, which is an LD driver by Toshiba Co., Ltd. is illustrated. Here, when the LD is operating and a constant input current is applied, the operating temperature increases and the optical output decreases. For example, when an input current of 110 mA is applied, the optical output is reduced from 40 mW at 25xc2x0 C. to about 20 mW at 70xc2x0 C. The reduction of the optical output causes a recording function to either deteriorate or not be able to be performed.
To improve such reduction, conventional LD drivers use an automatic laser diode power control (ALPC). In the ALPC, the output of the LD is monitored through an additional monitor diode and the change in the output of the LD is fed back. Accordingly, the output of the LD is maintained uniform. However, the ALPC function cannot be realized only by the LD driver, but it must be realized by an additional circuit or an integrated circuit (IC). Accordingly, electromagnetic wave interference may cause mis-operation during an interface operation when supplying the LD output control signal provided by the ALPC to the LD driver. Furthermore, when recording speed increases, the interface operation may not be performed. The waveform of the LD is reduced to either 780 xcexcm (in the case of a CD), 635 or 650 xcexcm (in the case of a DVD), or 40 xcexcm as a result of development of recording technology and increase in capacity. If a recording and reproducing apparatus includes a plurality of LDs, which lower compatibility and share between a recording medium, multiple circuit blocks for the ALPC corresponding to the respective LDs are necessary. Accordingly, a plurality of circuit blocks performing similar operations must be included. This is a big obstacle to making products small, light, and inexpensive.
Various objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The present invention is achieved by providing an objective lens for high-density focusing. The objective lens is a single lens having a high numerical aperture (NA). The objective lens is included in an optical pickup that also includes a relatively thin optical disk.
Accordingly, it is an object of the present invention to provide an apparatus and method including switches turning on and off driving potentials, each switch corresponding to the power level of the laser signal according to the channel control signals. A multiplexer multiplexes the driving potentials and outputs a multiplexed signal. A monitor diode monitors the power level of the laser signal and outputs a monitor signal. Further, a sample and hold unit samples and holds the monitor signal and outputs a signal indicative thereof. A differential amplifier calculates a difference between a reference signal corresponding to the power level of the laser signal and the output signal from the sample and hold unit. An adder adds the difference and the multiplexed signal and outputs therefrom a driving signal to drive the LD.
Furthermore, it is another object of the present invention to provide for a method receiving channel control signals to control different power levels of a laser signal from the LD; turning on and off driving potentials corresponding to the power level of the laser signal according to the channel control signals; multiplexing the driving potentials and outputting a multiplexed signal; monitoring the power level of the laser signal and outputting a monitor signal; sampling and holding the monitor signal and outputting a signal indicative thereof; calculating a difference between a reference signal corresponding to the power level of the laser signal and the output signal from the sampling and holding; and adding the difference and the multiplexed signal and outputting therefrom a driving signal to drive the LD.
Furthermore, it is another object of the present invention to provide for a method of driving an LD, including determining a type of a loaded recording medium; and setting driving potentials corresponding to power levels of a laser signal output from the LD according to the determined type of the recording medium.
Furthermore, it is another object of the present invention to provide for a method of compensating for a bias driving potential of an LD driver according to a change in a power level of a laser signal from an LD in a recording mode, including storing the bias driving potential; detecting a change in a bias power level in the laser signal; and compensating the bias driving potential according to the detected change in the bias power level.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.